Various obstacle detecting technologies have been developed, and have been used in vehicles to detect and remind a driver obstacles and/or pedestrians in the vicinity of a vehicle. Some solutions are based on radar, some solutions are based on multiple cameras, some solutions are based on laser, and some solutions are based on infrared cameras, but these solutions have a same drawback which is high cost. Although some conventional solutions using a single normal camera based on vertical edges of obstacles are low cost, these solutions generate too many false positives, especially when there are patterns on the road surface which patterns have edges substantially pointing to the focal point of the camera in a top view image. In view of the above, there is need to provide a more robust method and system for detecting obstacles using a single normal camera.